Hello. I have a problem. It created a little smoke last weekend and burnt up my nichrome wire (it was 8 ohms, now it's 32 ohms), also melting my high-temperature JB weld in the process, but that's another story.

The Extruder Excerciser program in reprap-host doesn't seem to give the right temperature. When the thermistor is in 28 C ambient, it reads 19 C. When the thermistor is in boiling water, it reads 26 C, and when it's in ice water, it reads 17C.

I know my circutry is working correctly, because the thermistor test program at the end of [reprap.org] works correctly when I replace the temptable with the EPCOS 100K table from the Thermistors page (http://reprap.org/bin/view/Main/Thermistor).

Things to note:
* I'm using the single arduino firmware V1.3.
* I was careful to edit the 'ThermistorTable.h' file in /hardware/libraries/ThermoplastExtruder to reflect the EPCOS 100K table used in the test.
* I know the "Extruder Excerciser" is communicating with the arduino, because I can turn the extruder motor on and off with it.

Any thoughts? I'm about to rebuild the metal parts of my extruder again, and it would be great we could find the culperit before I break the new one. Thanks for your help

It would really help if someone with a working RepRap that uses a thermistor could post the values of R1 and R2 that are actually on their board, together with their ~/.reprap/reprap.properties file and their .../reprap-arduino-firmware-1.3/library/ThermoplastExtruder/ThermistorTable.h file.

Comparing working versions of those files with my own might let me know if it is a configuration problem or something more illusive.

That is what I have and I get reasonable results. No good putting up my Thermistor table because it is different to yours.

I had a little trouble setting mine up. In the end I fitted 2 thermistors one of which I use to check temperature by measuring resistance. I found a table on the thermistor manufacturers site that gave resistance/temp data. It was pretty coarse but you could interpolate readings to get a pretty good idea of temperature.

Wow.. I feel stupid... That was the problem. Now, cool iced water gives 5C (probably wasn't in thermal equilibrium yet) and boiling water gives 96C. Yay.

Why aren't we using the Beta and Rz associated with the actual thermistor? Or, if these parameters are meant to be some sort of constants, why are they visible to the end user? Does this have something to do with the PIC/arduino transition? If so, would it be possible to have a check box that says "Using an Arduino?" and then when it's clicked, those three confusing parameters disappear from the settings box? That would be nice. There have to be others out there beside myself that aren't good at following directions.

These parameters are due to the PIC/Arduino transition. It makes the Arduino emulate the PIC as that was what the host software was actually written for. Over time I guess the host will develop in a different way as the Arduino becomes the focus of hardware development.

Your also right that it would be nice to have a check box but you must remember the software is largely a voluntary effort and things are in a constant state of flux.

I think Zach has put an enormous effort into the Arduino software and documentation for which I for one am extremely grateful.

Many others have also given freely of their time and certainly without the community help I certainly would not be where I am with Reprap (which out of interest is getting close to being able to build my first part)

If you really want to change something the source is always available for DIY hacking and if it is of benefit I am sure the mods would be incorporated into the release code.

I AM pretty sure that '.../reprap-arduino-firmware-1.3/library/ThermoplastExtruder/ThermistorTable.h' and '~/.reprap/reprap.properties' are not supposed to be kept in sync. The values in ThermistorTable.h are supposed to reflect the actual physical thermistor used, while the values in reprap.properties are supposed to be set to certain values no matter what thermistor you use (if you're using an Arduino based system). It's confusing, and should be addressed.

Does that at all relate to your problem?

I, personally, am not in the software-editing stage right now (I currently have my hands full with work and building the robot itself), so I cannot make the software change. I expect that, as support for the older pic-based-electronics are phased out, this aspect of the properties dialog in reprap_host will be more Arduino friendly.

Andromodon Wrote:
-------------------------------------------------------
> Are these two files supposed to be in sync? I'm
> not sure.
>
> I AM pretty sure that
> '.../reprap-arduino-firmware-1.3/library/Thermopla
> stExtruder/ThermistorTable.h' and
> '~/.reprap/reprap.properties' are not supposed to
> be kept in sync. The values in
> ThermistorTable.h are supposed to reflect the
> actual physical thermistor used, while the values
> in reprap.properties are supposed to be set to
> certain values no matter what thermistor you use
> (if you're using an Arduino based system). It's
> confusing, and should be addressed.

Andy,

Agreed on this: ThermistorTable.h must hold the values for the actual components.
But (if I got it right), the Arduino emulates the PIC by converting the temperture to a clock count to make the host happy.

This is done in routine calculatePicTempForCelsius: It converts a Celsius temperature to an estimated thermistor resistance which is then converted to a clock count. The resistance formula uses the parameters in ThermoplastExtruder_SNAP_v1.h and these must match the ones in the host, since the host will use the inverse formula to get the temperature.